I think the triangle/rectangle thing does not matter much. (actually, one side more, should that increase the polygon count? ;-) When you model in the Vertex Modeller (which I am learning) you can make a start with much less polygons. Recently I exported an .obj from a Vertex Modelled pillow (for UVMapper) with the slider set to 200. I almost blew up my double processor Mac trying to convert the resulting pdf to a .psd. Setting the slider to 0 still gets me a pillow (it is a subdivision smoothed thing), and the poly count almost looks professional. So maybe the export options are something to consider.